This invention relates to a channel associated signalling (CAS) compatible telecommunications node and software platform therefor.
There are two common digital communications formats; firstly T1 which is a 24 channel format utilised in the US and Japan and secondly E1 which is a 30 channel format utilised in the rest of the world. The T1 standard is set by the American National Standards Institute (ANSI) and runs at a clock rate of 1.544 Mbits/s. The E1 standard is set by CEPT (the conference of European postal and telecommunications administrations) and operates at a clock rate of 2.048 Mbits/s. In T1channels signalling is carried within each of the 24 time slots whereas in E1 channels signalling is carried within time slot 16.
CAS is a signalling protocol, the fundamentals of which will be explained in this section, with reference to FIG. 1, although many national variations apply. CAS protocols are approved by a number of standards bodies including ITU (International Telecommunications Union) and ETSI (European Telecommunications Standards Institute).
As mentioned above in the E1 format a connection is split in time into 32 individual time slots in which time slot xe2x80x9c0xe2x80x9d is used for frame signalling information and channel 16 is used for line signalling information. Register signalling is also incorporated on individual time slices as bearer information within the frame, or as pulsed charges in channel 16. Time slot or channel 16 is divided into sub-channels, each of which relate to the correspondingly numbered channel within the frame. Line signalling information regarding each of the channels within the frame is transmitted in channel 16 within the corresponding sub-channel. Each of these sub-channels transmits four bits of information, which for historic reasons are termed A, B, C and D bits.
These digital bits are utilised to indicate to the receiving node information such as:
The line is idle;
Trunk seizure is requested;
Trunk seizure is accepted;
Connection signal;
Clear signal;
Released signal;
In each of the different national GAS protocols different binary codes may be used to signify each of these requests, e.g. an xe2x80x9cidle linexe2x80x9d signal may be xe2x80x9c00100xe2x80x9d in one national CAS and xe2x80x9c0101xe2x80x9d in another national CAS, for example.
National CAS protocols may also differ in that a line signal may be continuous in some and pulsed in others. Also, register signals may be compelled that is a request is required in some systems and not in others. In some CAS systems a timer is set when a signal such as a request for a line is sent and a fault is determined when a response (either negative or positive) is not received within a predetermined time.
A very simplified process of making a telephone call utilising a compelled CAS protocol as discussed above is illustrated in the flow diagram of FIG. 2. This diagram is included to give an indication of the process through which a CAS protocol is used to make a call. However, it should be noted that this is a considerably simplified version and a host of information which is available through CAS such as billing information, metering information, call party status, for example, is not indicated.
With reference to FIG. 2 for a simple CAS protocol, when a channel, for example, channel 1 in a frame is not being utilised to make a call a line signal xe2x80x9cIdlexe2x80x9d signal is transmitted in the corresponding sub-channel 1 (block 40). If a first node (node A) wishes to utilise channel 1 it will send a xe2x80x9cSeize (SZG)xe2x80x9d signal in said sub-channel 1 (block 42). On receipt of this xe2x80x9cSeizexe2x80x9d signal at a connected node (node B) if the use of this channel is acceptable to node B, node B will send a xe2x80x9cSeize acknowledge (SZA)xe2x80x9d signal (block 44). On receipt of said xe2x80x9cSeize acknowledgexe2x80x9d signal node A will transmit a first digit of the telephone number of the telephone to which ultimately node A wishes to make a connection (block 46). This is the first register signalling signal which is sent on the channel 1 as opposed to the sub-channel 1 within channel 16. On receipt of said first digit of a telephone number node B will send a request for the next digit of a telephone number (block 48).
These requests and telephone digits are transmitted until node A sends the final digit of a telephone number (block 50) at which point node B may connect the line to the telephone. in question and send a xe2x80x9cConnect Call Chargexe2x80x9d signal to node A (block 52). After the telephone in question is placed off-hook an answer signal may be sent by node B to node A (block 54) and voice communication on channel 1 of the time frame may be established between the two nodes (block 56). This will continue until the phone is placed on-hook again at which point node A will send a xe2x80x9cClear Forwardxe2x80x9d signal to node B (block 58) upon receipt of which node B will send a xe2x80x9cRelease Guardxe2x80x9d signal to node A (block 60). At this point both nodes will continue to retransmit the original idle signal (block 40).
In FIG. 2, the indication as to whether or not signals are commonly line signals or register signals is indicated by the letter L or R to the left of the blocks. Line signalling is commonly utilised for control information whereas register signalling is typically utilised for call information. Different systems may be used although a common one is a dual tone multi-frequency system transmitted along the individual time frames.
As was discussed above, the binary line signal codes or tones for each of these signals may be different in different national CAS protocols and the duration for which they are transmitted may be different. The time interval before a reply or response is expected may be different and the overall waveform used in each signal may be different.
In known systems the operation of a node in compliance with the national CAS standard is determined by hard coding the operation of the node which requires a massive amount of rewriting of software in order to adjust a node for operation in compliance with a different national standard. For example, in order to provide a digital switch for use in a country utilising a CAS protocol for the first time, may take six or more months of intense software development as well as a vast amount of finance and manpower. Therefore, it is a huge commercial problem for telecommunications companies wishing to sell a client a switch for a new country if software has to be rewritten so that the switch will operate in that country. To date no solution to this problem has been found. Also, as there are so many legacy switches and PBXs in the field all operating on different national CAS protocols, CAS signalling can not be completely superseded by other protocols such as CSS7 or PRI.
It is therefore an object of the present invention to provide a CAS software platform which allows flexible relatively fast and relatively low cost CAS development.
It is a further object of the present invention to provide a CAS software platform which allows easy extension for new functionality.
It is a further object of the present invention to provide a telecommunications node and a system comprising said nodes with the aforementioned CAS software platform characteristics.
According to a first aspect of the present invention there is provided a Channel Associated Signalling (CAS) compatible telecommunications node, comprising an operating program in which CAS signalling information is separated from functional behaviour information which defines the behaviour of the node, such that adjustment of the operation of the node can be achieved through datafill.
Preferably, the CAS signalling information and the functional behaviour information are stored in mapped look-up tables in which specific signalling information is mapped to corresponding node behaviour information.
Most preferably, the CAS signalling information includes line signalling information and register signalling information. Preferably, the CAS signalling information also includes signalling waveform characteristics.
Preferably, the node behaviour information includes actions to be taken by the node in receipt of specific CAS signals and protocol timing characteristics.
Preferably, additional functionality can be added to the node by datafilling both the signalling information look-up table and the node behaviour look-up table with the necessary information and mapping the new information as required. In one embodiment the node is a switch. In another embodiment the node is a private branch exchange (PBX).
According to a second aspect of the present invention there is provided a Channel Associated Signalling (CAS) compatible telecommunications system comprising at least two CAS compatible telecommunications nodes, wherein each node comprises a CAS software platform in which CAS signalling information is separated from functional behaviour information which defines the behaviour of the node, such that adjustment of the operation of the node can be achieved through datafill.
According to a third aspect of the present invention there is provided Channel Associated Signalling (CAS) software platform, for control of a CAS compatible telecommunications node, in which CAS signalling information is separated from functional behaviour information which defines the behaviour of the node, such that adjustment of the operation of the node can be achieved through datafill.
According to a fourth aspect of the present invention there is provided a method of manufacture of a Channel Associated Signalling (CAS) compatible telecommunications node comprising the steps of:
storing CAS signalling information and corresponding node behaviour information
in separate look-up tables;
mapping entries in the signalling information table to corresponding entries in the node behaviour table; and
adjusting the operation of the node by altering selected entries in either of the look-up tables.
Preferably, the method includes creating a framework software platform containing International telecommunications Union ITU-R2 standard compatible signalling information and node behaviour in respective look-up tables and adjusting the tables in order to conform to separate national variations on the aforementioned standard.
The method of claim 16, wherein additional functionality can be added to the node by datafilling both the signalling information look-up table and the node behaviour look-up table with the necessary information and mapping the new information as required.
It is an advantage of the present invention that the software platform enables a quick and easy ,means of defining the operation of the node to comply with the specific task protocol through datafill.
It is a further advantage of the present invention that adjustments for national CAS protocols may be made via datafill.